The present invention relates generally to a wafer carrier. More particularly, the present invention relates to a wafer carrier with a wear indicator for use in disk polishing processes.
Hard disk drives used in computers or similar devices contain aluminum or ceramic disks for storing data. As the need to store increasingly more information on the disks increases, the disks must have extremely smooth and flat surfaces. Similarly, wafers used in fabricating components used in computers are also required to exhibit extremely smooth and flat surfaces to facilitate the extremely close placement of the components on the wafers. “Disk” when used herein includes the substrates utilized for hard disk drives as well as the wafers for manufacturing semiconductor components.
Since it is typically not possible to directly fabricate such disks with the requisite levels of smoothness and flatness, the disks must be polished to obtain the desired levels. During the polishing process, the disks are placed in a consumable flat disk carrier that is used to transport the disks through the polishing process. The disk carrier has a plurality of openings therein that are each adapted to receive one of the disks. The carrier with the disks therein are placed in between platens of a polishing equipment and are rotated as the platens are moving. To facilitate the controlled rotation of the disk carriers in the polishing apparatus, the disk carriers typically have a circular shape and a plurality of gear teeth extending from an outer edge thereof.
Disk carriers have previously been fabricated from sheet metal. While the metal disk carriers provided a high level of support to the disks during the polishing process, the metal disk carriers produce an undesirably high level of abrasives during the polishing process.
In an attempt to overcome the limitations associated with metal disk carriers, disk carriers have been fabricated from fiberglass-reinforced epoxy. These types of disk carriers are typically fabricated using thermoset resins that are molded using composite lay-up techniques. While these types of disk carriers provide desirable strength characteristics, the polishing process causes fiberglass particulates to be released from the epoxy-glass composite disk carrier. Such fiberglass particulates act as abrasives during the polishing process, which scratch the disk surfaces and thereby increase the disk rejection rates, in many instances approaching 15 percent disk rejection.
These disk carriers exhibit severe wear in the gear tooth region. As these disk carriers wear, increasing amounts of fiberglass are released into the polishing slurry. Once the rejection percentage exceeds a threshold level, the fiberglass reinforced epoxy disk carriers are replaced.
Non-abrasive disk carriers, may not exhibit such significant levels of wear in the gear tooth region. Rather, degradation of the non-abrasive disk carriers is often evidenced by tooth failure where one or more of the teeth break off resulting in a crash during the polishing operation. The tooth failure can be corrected to wear off the surface of the carrier.
For example, Winings, U.S. Pat. No. 4,239,567, discloses forming the disk carrier with a polyurethane upper surface. Popovich et al., U.S. Pat. No. 5,882,245, discloses forming the base disk carrier from polyetheretherketone by extrusion, rolling or calendaring and applying additional layers or coatings on the base disk carrier. These two patents are incorporated herein by reference.
One technique that is frequently used to track the life of the disk carrier is to count the number of times that the disk carrier has been used. Once the disk carrier has been used a specified number of times, the disk carrier is replaced. Typically, the disk carriers are replaced after 100 uses.
Although it is presumed polishing disk carriers are consumable, it is economically advantageous to obtain as many uses of the disk carrier as possible without effecting yield. Optimal life expectancy of disk carriers may be empirically determined and such life expectancy can be correlated with wear. Wear indicators for laminations of laminated polishing disk carriers are known. Popovich, supra, discloses placement of an adhesion promoter on a 0.5 mm thick base sheet of polyetheretherketone, applying or printing a geometric pattern such as lines, dots, or figures, and then laminating a 0.05 mm thick film of resin thereon. Popovich identifies that observation of the geometric pattern provides a simple method for visual inspection of the integrity of the coating on the base and provides no means of measuring wear of the base portion of the wafer carrier nor prediction of failure of the wafer carrier.
A simpler and more versatile method and system is needed to monitor wear of polishing disk carriers. Such a method should provide incremental indication of the useful life cycle of the carrier.